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# Epic Science Fair Project? Answered

Okay, Okay I won't do the Digital Taste project anymore. But I need help with a new one. I am in grade 10, but i have a good understanding of arduino and programming. What projects could I do? I really only want answers about electronics or programming, as those are some of my areas of skill. So what could I do? I'm looking for innovations possibly, or really cool things remotely related to science. If possible, it should cost under \$100 to make a basic working prototype, and I already have basic arduino electronic parts.Thanks.

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## Discussions

There is a distance sensing module, made for use with Arduino, which measures distance, by way of the time-of-flight of a pulse of ultrasonic sound through air.

This module is intended for measuring distance, but I imagine it could also be used to measure the speed of sound, through air, or some other gas sample.

The speed of sound c through an ideal gas is predicted to depend on just three numbers: temperature T, molecular weight M, heat capacity ratio gamma.

c = (R*gamma*T/M)^(1/2)

where R is a natural constant.

See Wikipedia page titled, "Speed of sound" for a more complete explanation of this, here:
https://en.wikipedia.org/wiki/Speed_of_sound#Speed...

Two of those numbers, {c,T}, can be measured with arduino hardware, namely that distance sensing module, plus some temperature sensors. The remaining variables {M, gamma} are characteristic of the gas itself.

So I think the most simple, and inexpensive, science project you could build with {Arduino + distance sensor + temperature sensors} would be an experiment to investigate the temperature-dependence of the speed of sound in ambient air.

That is to say you set this thing up with a fixed-distance reflector, and you let the temperature change around it, and see if you can discover any T-dependence in your measurements of c.

http://www.toptechboy.com/arduino/lesson-17-measur...

gives an overview of wiring the module to Arduino, and the sketch for measuring the TOF (time-of-flight) of the sound pulse, and the formula for converting this to speed; i.e.

c = 2*D/TOF

where D is distance to target, and TOF is time of flight for the sound pulse.

Also by the way, I think the name of this module is usually HC-SR04, and the names of its pins, { Vcc, trig, echo, GND}, and I have seen it, or copies of it, on eBay, and other places that sell modules for Arduino.

Once you have discovered all you can learn from measurements on ambient air, I think the next step is put this setup, this uh, sound wave race track, into a container where you can experiment with gases besides air.

However that next step, is maybe a big next step in terms of expenses. I'm not sure what to build it out of. A gallon sized glass jar might work. The distance from the top to the bottom of such a jar is about 10 inches, or 25 cm. Or maybe you could build the gas container out of a length of PVC pipe?

I'm not really sure how much travel distance one needs to get a good measurement for speed of sound using this kind of TOF sensor.

Anyway, in addition to the gas container, some plumbing, {fittings, hoses, pumps maybe?, pressure measurement?} is needed to move gases in and out.

Note that pressure, gas pressure, is not a factor in that equation for speed of sound, c =(R*gamma*T/M)^(1/2), mentioned previously. So I would expect a container with air pumped out, via vacuum pump, to 0.5 or 0.1 that of ambient pressure, would have the same speed of sound, and that might be something interesting to investigate.

Some bottled gases you can find, somewhat cheaply, on the street, include helium (for balloons), and carbon dioxide (for paintball, some pneumatic power tools).

http://www.engineeringtoolbox.com/speed-sound-gase...

the speed of sound, at 0 celcius, in various gases.

By the way, I think these differences in speed of sound, are the basis for the old parlor trick of making one's voice higher pitched, by inhaling helium (He), or making one's voice lower pitched by inhaling sulfur hexafluoride (SF6).

The lower voice trick is less commonly seen, as a lot of party stores sell He-filled balloons, but not SF6-filled balloons. Perhaps heavier-than-air balloons are perceived as less festive, not a big seller, except maybe to physics and chemistry teachers.

Great Idea! Do you mean something like this. I Do have two of these, and a Thermister. How would you recommend heating/ cooling the gas. I have a peltier module, but i doubt that would work.

Oh. Hey. I was just thinking: instead of this indoor-outdoor stuff to effect a temperature change, it might be just as easy to put your setup in a portable ice-chest,

https://en.wikipedia.org/wiki/Cooler

you know an insulated box, with a bag of ice in it. Something like that.

I was sort of imagining that your heating and cooling could be by done by ambient conditions, like the difference between daytime and nighttime temperatures, or the difference between indoors and out.

Actually, since you said you have some of these distance measurement modules, you probably have enough hardware to some preliminary investigations into whether or not this project is feasible.

What I suggest you try first, is putting together the setup described on that page I linked to previously,
http://www.toptechboy.com/arduino/lesson-17-measur...

with two modifications:

(1) the distance sensor module is looking at a target at some fixed distance; e.g. both the sensor and target are bolted, attached, into some kind of frame, like a wooden crate

(2) the frame is portable enough to carry it outside, where the air is colder

Step (2) might be tricky if you're using a desktop PC to look at the serial output. Or maybe you've got a LCD module, and you can direct the output to that instead, and make the whole setup portable?

Actually I'm not sure of the best way to get this setup outside. By the way, I have roughly zero hours of experience building things with Arduino. I always wanted to learn about this though. Maybe I've been putting it off, I guess.

Anyway, the motivation for getting the thing outside, is I am hoping you can get about about a 10C or 20C difference in air temperature, between indoor and outdoor air. Usually the coldest time of day, is early in the morning. Here's a Wunderground forecast, for next week, for "ottawa, canada",

https://www.wunderground.com/cgi-bin/findweather/g...

For the change of speed of sound in air, I am expecting roughly a 6 m/s increase for every 10C of temperature increase. More specifically, if I take, from the Wikipedia article "Speed of sound", that formula, "Practical formula for [speed of sound in] dry air", then feed that to Octave,
http://www.gnu.org/software/octave/
http://octave-online.net/
like so:
>>> Tc=[0;5;10;15;20;25]; c_air=331.3+0.606*Tc; [Tc,c_air]
ans =

0.00000 331.30000
5.00000 334.33000
10.00000 337.36000
15.00000 340.39000
20.00000 343.42000
25.00000 346.45000

I mean those are the approximate numbers I would expect to see for the speed of sound in air as a function of temperature. The column on the left is temperature in degrees C. The column on the right is speed, in meters per second.

http://www.phy.mtu.edu/~suits/SpeedofSound.html

I *think* are roughly the same numbers.

Which reminds me, regarding units, the example sketch in, lesson 17, at "toptechboy.com", I linked to above, for some strange reason that guy was doing all his measurements in imperial units, like inches, and miles per hour. Seriously!? In your sketch, I recommend using honest SI units like meters, and seconds, and meters per second. You know, for example, if the distance to your sound-reflector target is 15 cm, that's 0.15 m.

I guess that's three mods: (1) make the target distance fixed, (2) make it so you can carry it outside, (3) change the units in the calculations in the sketch to SI units

Anyway, if this preliminary stuff is successful; i.e. if this setup seems to show faster speed-of-sound in warmer air, then maybe it is time to go shopping for some better temperature sensors, like maybe some digital temperature sensors, e.g. DS18B20.

Sort of the neat thing about those, the DS18B20, is you can put like a bunch ( I saw an example somewhere, using 5 of them) , measure temps in several different places, using just one IO pin! Although the code for doing this looked a little complicated, to me. Like I said previously, I have close to zero experience working with Arduino, so you might be kind of scratching your head at me recommending hardware to you.

Actually, I was looking for a page that compared different options out there for temperature sensors. I found some chatter on this page, but I'm not sure if its comprehensive.
https://www.intorobotics.com/pick-best-temperature...

Also on the shopping list is maybe a SD card module, so you can leave your setup to sit around for hours at time, and let it collect data for you and write it to the SD card.

In the event that the easy preliminary setup is NOT successful, if you do not see a trend of slight increase in speed-of-sound with temperature, then... I dunno. It might mean this distance sensor thing is buggy, or noisy, or somehow not suitable for actually measuring the speed of sound in gases. I mean, if it turns out this thing is really hard to make it work the way we expect it to, it's better to find that out early in the game.